Signaling system for radiotelephones



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SIGNALING SYSTEM FOR RADIOTELEPHONES Filed May 26, 1934 4 Sheets-SheetvZ JIIIIIIII IIIIIIIIIL IaHII- www E222 im 65:1*

Pif/Em I ATTORNEY G QQ.

Dec. 22, i936. E. R. TAYLOR Er AL SIGNALING SYSTEM FOR RADIOTELEPHONES Filed May 26, 1934 4 Sheets-Sheet 5 n@ ik Dec. 22, 1936. E. R. TAYLOR Er AL SIGNLING SYSTEM FOR RADIOTELEPHONES Filed May 26, 1934 4 Sheets-Sheet 4 www mw @w mM/mgm 06a m m WL. A

Patented gec. 221, 11936 NiTED STATES TENT OFFICE SGNALING SYSTEM FOR RADIO` TELEPHONES York Application May 26, 1934, Serial No. 727,800

4 Claims.

This invention relates to radiotelephone or land wire transmission systems, to transmission -of signaling pulses for alarms, controls or tele graph and to selective signaling means for use on such systems. More particularly it relates to arrangements or selectively calling any one of a number of stations in such systems Jfrom a central point, and in certain cases from any other station. Stations may also be called in groups. Likewise the selective apparatus may be used for other control arrangements and the means for transmitting the signal pulses may be utilized for other purposes.

In operating a radiotelephone circuit, such as a harbor radiotelephone system, it is necessary that a. central station be able to call any one of the boats, and that the boats be able to call this central station. It may also be desirable for a boat to be able to call other boats. It also is essential that the calling of any boat by a central station be extended to a toll switchboard position permitting a toll operator to handle traffic efficiently over this system. In certain leased wire full or partial period talking circuits set up on land wires similar calling arrangements between the stations by using voice-frequency transmission of the signaling pulses may be required. It is also desirable to call the stations in large groups in cases of emergency or in smaller groups as the more eicient means for broadcasting information. The signaling system of this invention is designed to meet the requirements outlined above.

As is well known, a radio transmitter and radio receiver may be connected by means of a combination of four-wire and two-Wire circuits to a twowire terminal at a switching point where connections may be established by a switching operator between the radio channel and various telephone circuits. It is also well known that terminal ampliers, voice-operated devices, and other apparatus under the control of a technical operator may be associated with the four-wire circuit in such a manner that echoes and singing, which might be caused by radio or wire line unbalances, are eiectively eliminated, and radiation by the radio transmitter of signals received by the radio receiver is prevented.

Likewise on shipboard a four-Wire circuit may be made up of a radio transmitter on one branch, a radio receiver on the other, and various controls and necessary auxiliary apparatus.

In accordance with this invention circuit arrangements are provided whereby pulse send- (Cl. Z50-6) ing equipment is associated with the four-wire land terminal, control of which is located at the terminal and is also extended to a distant toll switchboard. This pulse sending equipment sends spurts of 150G-cycle tone under control of a dial or selector key, and also controls thev terminal in such a manner that static crashes on the receiving branch may not break up the pulsing. At the ship end of the circuit a selective receiving ringer is connected to the output of the radio receiver causing an alarm when the code for that particular ringer is sent in spurts of 150G-cycle tone. Arrangements may also be set up to send pulses from the boat to signal other boats and the land station. Several combinations of these arrangements together with automatic calling-in of the land station under control of the ships carrier are possible. It will be understood, of course, that the arrangements used at the ship and shore stations may be any of many well-known arrangements and that the invention is not to be limited to a ship-to-shore radiotelephone system.

The invention may now be more fully understood from the following description whenread in connection with the accompanying drawings, Figure 1 of which shows the circuit arrangement for one terminal of the radio system embodying the signal sending arrangements; Fig. 2 of which shows a circuit arrangement embodying the signal receiving unit which may be used for one or more radio stations to be communicated with; Figs. 3 and 5 show modified forms of signal transmitters; Fig. 6 shows a modied form of signal receiver; and Figs. 4 and 7 show modied forms of terminal arrangements particularly adapted for use aboard ships.

Referring to Fig. 1, SL designates the twowire line connecting the control station to the switchboard. The two wire line SL is connected through a hybrid coil, HB1, to a transmitting.`

path TLi, and a receiving path RLi, being balanced by a suitable network N1. Path TL; and the following parts of the transmitting circuit include the transmitting volume control variable attenuator TVC, amplifier TA, hybrid coil HB2,

v transmitting path TLz, transmitting path TLa,

transformer T1, and radio transmitter RT1. The receiving path includes receiving amplier RAz, radio receiver RR1, receiving path RLz, transformers T3 and T4, resistance termination RTz, receiving volume control attenuator RVC, amplier RA1 and receiving path RL1.

In order that when transmission is taking place over either the transmitting or receiving path the other path will be disabled, echo suppressor devices are associated With each path. The echo suppressor associated With the transmitting path TL1 comprises an amplifier-detector unit TAD, of a well-known type, with its input connected through Variable attenuator TSC and band-passi filter F1 to hybrid coil HB2 in conjugate relationship with transmitting path TL2, the output of amplifier TA being balanced by a suitable network, N2. The output of the amplifier-detector unit TAD controls through master relay TM the relays TSS and TEHO for performing the blocking or disabling operations whereby transmission is permitted in only one of the paths TL2 and RLi at a time. Normally, transmission path TL2 is disabled by the back contacts of relay TSS, which short-circuit the conductors, and transmission from transmission path TL1 to, the radio transmitter can not take place. Blocking means comprising transformer arrangements T3 and T4 are associated between receiving lines RL1 and RL2. These disabling means comprise transformer arrangements which are so connected as to be balanced When the contacts of relay TEHO are opened, thereby preventing transmission through the transformer arrangements. When the contacts of relay TEHO are closed, however, the transformer circuits instead of being balanced are, in effect, connected so as to be parallel-aiding, thereby permitting transmission to take place readily. Normally, relay TEHO (which is controlled by the amplifier-detector TAD) is deenergized so that the receiving path is unblocked to permit transmission to take place from receiving path RL2 tot the two-wire line SL.

The input of an amplifier-detector arrangement RAD is connected through band-pass lter F3, receiving sensitivity control RSC and resistance termination RT1 to the secondary windings of transformer T4, so as to be effectively in series with the resistance termination RT2 in the receiving path RLi, and has in its output a relay RM, which when operated opens the control circuit from the amplifier-detector TAD to switching relays TSS and TEI-IO, thereby maintaining the transmitting path TL2 blocked and receiving path RL1 unblocked when signal currents are being received from the radio receiver. Static or other interference is prevented from causing operation of relay RM duing idle periods by the action of relay COD which maintains a short circuit on receiving path RL2 Whenever receiving carrier f2 is not present. As will be explained later in connection with Fig. 2, the distant or boat transmitters are so arranged that carrier frequency f2 is radiated only when communication from a boat to the shore is desired. The control circuit of relay COD includes the following. The input band-pass lter F4 which passes substantially only carrier frequency f2 is connected in multiple with the input of radio receiver RRi, and the output of filter F4 is connected to the input of detector CD, the D. C. output of which controls the operation of relay COD. The operation of the apparatus so far described for signal transmission is as follows:

Signal currents incoming over the two-wire circuit SL pass through the hybrid coil HB1 and through the amplier TA. Some of the energy enters the amplifier-detector unit TAD and causes relays TM, TSS and TEHO to be energized.

Relay TSS removes the short circuits from transmitting line TL2 while relay TEHO by operiing its contact causes the transformer arrangements T3 and T4 to block the receiving path. In the meantime, a part of the energy passes from hybrid coil HB2 through the transmitting paths TL2 and TLa to radio transmitter RTi and is transmitted o-n carrier frequency f1. The receiving amplifier-detector RAD associated With the receiving path cannot be actuated to disturb the circuit condition now existing because the receiving path is disabled in the manner already described.

If, in the normal condition of the circuit, car-` rier frequency f2 modulated with a signal is received through amplifier RA2, part of the received energy passes through band-pass filter F4 to detector CD, causing the operation of relay COD which removes the short circuit from the receiver RR1 and is demodulated, the resultant mainder of the received energy passes into radio receiver RRi and is demodulated, the resultant signals passing through receiving path RL2 and transformer arrangements T3 and T4. Part of the energy passes through receiving amplier RA1 and hybrid coil HB1 to the two-wire line SL. The remaining received energy passes through receiving sensitivity control RSC to the amplier-detector RAD to cause the operation of relay RM, which opens the circuit controlled by the amplier-detector unit TAD, thereby preventing energization of relays TSS and TEHO so that the transmitting path is disable and the receiving path remains unblocked while the signal currents are being received.

The apparatus and circuits employed at the ship station may be of several well-known types as, for example, those shown in Fig. 2. This shows an antenna normally connected to radio receiver RR2, which is arranged to receive carrier frequency f1, and the radio transmitter RT2 arranged to transmit carrier frequency f2. The antenna may be switched from the radio receiver RR2 to radio transmitter RT2 by relay AR, which is controlled by key AK. The output of radio receiver RRz is connected to operators receiver OR2 and the input of radio transmitter RT2 is connected to operators transmitter 0T2. Accordingly the operator at the ship station may normally receive signals transmitted on carrier frequency f1 and may transmit signals on carrier frequency f2 by operating key AK, which enables radio transmitter RT2 and disables radio receiver RR2. Thus carrier frequency f2 is radiated only when signals are to be transmitted from the boat. The signal receiving unit RUl is bridged across the output of the radio receiver along with the operators receiver OR2.

The apparatus so far described relates to telephonie or other communication between the two- Wire line SL and a distant radio station. The additional equipment and circuits which are associated with the shore terminal in order to aord dial signal transmission and alarm features will now be described.

Referring to Fig. l and the operation of the echo and singing suppressing means described above, it will be seen that relay TM must be operated whenever signals are transmitted from the two-Wire line SL or from the oscillator O1 to the radio transmitter RTi, and that relay COD must be operated whenever signals are transmitted from the radio receiver RR1 to the two-Wire line SL and, hence, one or the other of these two relays TM or COD must be operated whenever communication is attempted in 75 either direction of transmission. When relay TM is operated, relay RM cannot be actuated to disturb the circuit condition. Accordingly, in sending signal spurts from the central station, the signal tone is within the voice range and operates the relay TM. The operate contacts of relay TM are also closed to hold the circuit in the transmitting position. The operation of the circuit is as follows:

The 150G-cycle oscillator O1 is bridged across the input of amplifier TA through the high resistances HR1 and I-IR2. The oscillator output lis normally shorted through the pulsing contacts of dial D2, and the contacts of relay R4. When dial D2 is moved from its normal position, its lower contacts close, shorting the contacts of relay TM and operating relays TSS and TEHO. When dial D2 is released, its upper contacts are opened once for each unit of the digit dialed. This sends spurts of 150G-cycle tone through amplier TA and the remainder of the transmitting path in the manner already described. The lower contacts of dial D2 open when the dial returns to normal.

The sending of signals from the central station may be accomplished from a distant toll switchboard as follows:

Dial D1 and dial key K1 are connected through a telegraph repeater and line DCL1 tor relay R1. When key K1 is operated, relay R1 operates, in turn actuating the slow-release relays R2 and R2. Relay R2 shorts Vthe contacts of relay TM, operating relays TSS and TEHO. Relay R2 connects the upper contact of R1 to the winding of R1. When dial D1 is operated, relay R1 releases once for each unit of the digit dialed. Relays R2 and R3, being slow-acting, do not release, however. Therefore, relay R4 is operated by each release of R1 and 150G-cycle spurts are sent out as previously explained. When key K1 is released at the conclusion of the dialing period, a nal spurt is sent by the release of R1 before R2 has released. This is made use of as will be explained in connection with Fig. 2.

For giving alarms or signals when relay COD is operated, suitable circuits are set up to indicate that a call is desired by some distant station or that a distant station is answering after being dialed. The circuit includes the following:

The lower contacts of relay COD, key K2, relays R5, Re and Rv, key K3 and bell or buzzer B2 for giving an alarm at the central station and, in addition, line DCL2, relays Rs, R9 and R10, lamps L1 and L2 and bell or buzzer B1 for giving an alarm or signal at the switchboard. The operation of the circuit is as follows:

The operation of relay COD by carrier frequency ,f2 connects ground to key K2, thereby short-circuiting the winding of relay R5, which is normally operated as shown if key K2 is in its normal position, that is, with the contacts closed. Key K2 is provided so that the alarm arrangements may be disabled when alarm operation is not desired. Relays R5 and Rs are made slowacting in a well-known manner such as shortcircuited windings or the addition of a copper slug to the core in order that intermittent short duration operations of relay COD, such as might be caused by static, may not give an alarm. To continue the circuit operation, relay R5 releases, after a predetermined interval of time has elapsed, and its contacts close short-circuiting in turn, the windings of relay Re. VAfter a second predetermined interval of time, relay Rs releases, causing the operation of relay R7.

This, through its lower contacts, completes the circuit to the bell or buzzer B2, giving an alarm. If key K3 is in its normal position with its contacts closed, relay R7 will lock itself operated through its upper contacts and the alarm will continue until K2 is operated to break the battery circuit.

The remainder of the circuit operation required to operate the alarm and signals at the switchboard is as follows:

Relay Rs, in releasing, places ground on the line DCL2, causing the operation of relay Rs. Relay Ra through its contact operates relay R9, lights lamp L1 and causes bell or buzzer B1 to operate. Relay R9 locks up through the contact of relay R10 and the alarm and lamp will remain actuated until the operator at the toll switchboard places a cord in the line jack J 1 when battery flowing through the sleeve circuit will operate relay R111, permitting R9 to release and removing battery frorn lamp L1 and bell B1.

If the operator has placed a cord in the line jack and has dialed a ship she will receive an indication that the ship has answered by the lighting of lamp L2. The cord in the line jack has operated relay R10, and when relay COD is operated by the boat answering, relay R2 will be operated as previously explained, which will send battery through its contact and through the upper lower contact of relay R10 to lamp L2. During the period of a call, it is expected that key K3 at the central terminal will be operated so that further operation of relay R7 and bell or buzzer B2 will not occur as COD is operated. At the conclusion of each call, key K3 will be restored to normal. This will permit relay Ra to operate and light lamp L2 whenever relay COD operates for a length of time sucient to release relay Re. Intermittent flashing of L2 will therefore occur during conversation, but a slow steady flash of L2 for switchhook supervision may be obtained by the boat station operating and releasing at a slow interval the switch AK in Fig, 2.

Referring to Fig. 2, which represents the ship apparatus for ship-to-shore communication, the carrier frequency f1 modulated by the 150G-cycle spurts is received by radio receiver RRz, and when keys SH and AK are not operated the 150G-cycle output of RR2 enters the signal receiving unit RU1. This is essentially a twostage amplifier with a Volume limiter action having two tuned output circuits working into rectifying arrangements whose D. C. outputs are made equal and control a pulse dividing relay circuit. This circuit controls a railway selector in such a manner that one step of the selector occurs for a marking and spacing pulse together. The selector consists essentially of a polar relay with a ratchet attachment so arranged that successive operations of the relay at proper speed cause the stepping around of a contact wheel. Stop pins at certain points prevent the contact wheel from returning to its normal position when the regular sequence of stepping is interrupted at these points. Any interruption of the regular sequence of stepping when the contact wheel is at any other point causes it to release. The use of these selectors on railway telephone dispatch systems is well known. The speed of pulsing used in this system is about seven cycles per second.

The signal spurts of 1500 cycles enter the twostage? amplifier through the transformer IN. The permanent grid potential on the first tube is small and the input potential if of suflicient magnitude drives this positive, charging the condenser C1 and thereby lowering the gain. When the input is removed, the resistance LR1 discharges condenser C1 and the gain increases. These units are so chosen that the gain of the ampliiier increases somewhat during a spacing pulse while dialing. Also, the gain of the amplifier is lowered in a period of time which is longer than the operate time of relay R11. Dialing spurts tend to lower the gain and thereby decrease the static currents in the relay but the initial spurt of rectied current at the beginning of each marking pulse before the gain is lowered is large and by its action in operating relay R11 enables signaling through a higher noise level than would be possible without this action. When no dial sports are being received the static and voice currents lower the amplifier gain, thereby reducing in magnitude the peaks of rectified current in the balanced branches, helping appreciably to eliminate false operation from any unbalance which may occur vin the static or voice currents. This is particularly valuable in the case of voice currents where the characteristics of speech are such that there may be considerable frequency inequality.

The output of the first stage tube VT1 is impedance-coupled to tube VTz by resistance PR1, condenser C2 and resistance GR1. Tube VTz is transformer-coupled to two Rectox circuits RR11 and RR12 by means of two output transformers OT1 and 0T2. Transformer OT1 is tuned to 1500 I cycles by means of retard coil TR1 and condenser TG1 while output transformer 0T2 is tuned to 500 cycles by retard coil TR2 and condenser TG2. The rectified output currents are opposing when applied to relay R11, the current from OT1 being in the direction to cause relay R11 to operate while current from 0T2 is in the direction toi aid the permanent biasing current supplied through resistance BR1 and hold relay R11 in the nonoperated position. Noise and voice currents, therefore, tend to balance out and produce no operation of relay R11, although actual voice currents have such unbalanced frequency characteristics that occasional operation of relay R11 may occur particularly at the start of an exclamation before any gain regulation of the amplier occurs. The sensitivity of the ampliiier is such that relay R11 may be successfully operated for an input range from about 25 db. above 1 milliwatt to about 20 db. below 1 milliwatt.

Relay R11 is operated by a marking signal (spurt of 150G-cycle current) for each dial pulse. The biasing current returns it to the non-operated position fcr spacing pulses. With relays R12 and R13 in the position shown in Fig. 21 when relay R11 operates, relay R13 operates reversing the polarity across the condenser C3 and the selector winding and operating the polar relay in the selector RS while the condenser is charging. When R11 releases, R11 operates and R13 remains operated. When R11 again operates, R13 releases and reverses polarity on the selector RS while R12 remains operated. When R11 next releases, R12 releases and R13 remains non-operated. Thus relay R13 reverses polarity on and operates the polar relay in selector RS for each operation of relay R11 or for each unit of the digit dialed. The polar relay operates while the condenser C3 charges but releases when the charge completes. The condenser C3 and resistance unit CR1 are such that the polar relay does not release during the dialing of a digit (at the speed of pulsing used in the system) but does release between until the switch SH is operated; As mentioned above when dialing from the toll' switchboard, this final spurt is sent when the dial key is returned to normal by the operator. The key SH 110 bell will ring until a nal dialing spurt is sent ory is normally open but is closed when the handset is lifted from the switchhook. This key operates relay R14 which discharges the condenser Ca through the selector windings, causing it to operate once and return to its normal position. No operations of selector RS may occur while relay R14 is operated.

Returning to Fig. 1, the dial D1 being an ordinary telephone dial, signals by sending a marking and spacing impulse for each digit unit and is not capable of sending signals corresponding to digits of more than ten units. The railway selector of Fig. 2 is so arranged that where any particular station is to be called the selector respends to impulse in groups corresponding to a plurality of digits, as for example 3--7-7 vor fil-6 7. As each digit does not exceed ten pulses these digits may be sent by successive operations of the dial D1. Where, however, it is desired to select a group of stations, the dial D1 cannot ordinarily be used due to the limitations of the selector RS Which is so arranged that for group selection a continuous train'of pulses must be received which is equal in number to the sum of the pulses of the code digits of any individual station. In a system having a considerable num-`r ber of stations this will involve sending a continuous group of pulses greater than ten and hence the dial D1 is not adapted for group calling. A common arrangement of the selector is to make it responsive to group calls involving(- continuous trains of say 17, 19 or 21 pulses. Thus one group of stations might be set to respond to ya train` of Il pulses, another group to a train of 19 pulses, etc. The groups of stations might include in part the same stations, or one group might be a sub-group of the other.

The transmission of these large trains of impulses makes it necessary to supplement the dial D1 by one or more railway selector key sending units of the type shown at SK in Fig. 3, one` such unit being provided for each group to be called. Each selector key unit involves a code disc havin'g'a number of teeth suitably arranged to operate pulsing contacts. The dial may then be used for calling any one of a small number.:v

of stations and the selector key unit may be used to call a group. For a large system it will be preferable to omit the dial and use av master railway selector key of known type lboth for calling individual stations and for callingv groups. The master railway selector key is so arranged that by setting certainl combinations of keys the proper series of pulses for calling any individual station or any group may be sent.

If either the selector key unit or master rail,

way selector key is provided, since the dial D1" sends a marking and a spacing pulse for each unit of the digit dialed, whereas the selector key unit and the master railway selector key each send only one pulse (either marking or spacing),

for each unit of the digit, it will be necessary to provide the selector keys with pulse multiplying relays such as R21 and R22 of Fig. 3. These put out a marking pulse followed by a spacing Y pulse for each pulse sent by the selector key whether the selector key pulse be marking or spaclng.

'I'he operation of this circuit is as follows: When key SK turns so that its contacts close relay R21 operates. Battery iiows through resistance CR1, and the lower contacts of R21 to charge condenser C1. Relay R22 operates on this charge current, condenser C1 and resistance CR1 being so chosen that the time during which R22 remains operated is 1/2 that during which the contacts of SK remain closed. When the contacts of SK open R21 releases and C1 discharges through resistance CR2 and the windings of R22 causing R22 to operate for the same period of time that it operated when C1 was charging through CR1. Therefore, relay R22 operates and releases putting out a marking and a spacing pulse of equal length each time the contacts of SK close or open. The contacts of R22 are shown in series with a dial D1 shorting the output of an oscillator when A1 connects to A2 and B1 to B2. Spurts of tone will be. sent from the oscillator as R22 operates or the dial opens its contacts. If remote control of the oscillator is desired as shown on Fig. 1 the contacts of the dial D1 and relay R22 may be placed in series between key K1 and telegraph repeater 'I'R as shown in Fig. 3 by connecting A1 to A3 and B1 to B3 in which case the telegraph'circuit will be controlled directly instead of the oscillator output. This control may then be applied to a distant oscillator in the manner shown on Fig. 1 and explained previously. It should be noted that the combination of dialing equipment and oscillator may be used with central control equipment as shown on Fig. 1, or may be multipled with operators transmitter 0T2 as in Fig. 4 and used to modulate radio transmitter RT2 or. may be associated with any signal transmission system which will transmit the frequency output of oscillator O1.

The circuits shown in Figs. 1 and 2 are arranged for ship-to-shore communication and hence the shore station sends on frequency ,f1 and receives on frequency f2 while each ship circuit as shown in Fig. 2 sends on frequency f2 and receives on frequency f1. For communication between ships it is desirable that a diiferent frequency be used as otherwise the supervisory signals B1 and B2 of Fig. 1 would be operated at the shore station every time a call between ships took place. Hence the ship stations should be arranged to transmit and receive on some third frequency f3 for intership communication as shown in Fig. 4 in which a separate set of transmitting and receiving equipment is provided for communication between ships.

Y If we now consider Fig. 4 we see a ship sta- 'tionarranged for two-way selective signaling input being shorted except when these contacts open once for each unit of the digit dialed.

Key DK also-operates relays R15 and R16, R16 in turn operating R14, R11 and AR. R16 connects the tuned output transformer OT1 primary winding through its lower contacts and condenser vC5, resistance FBR and inductance FBI to the input transformer providing a feedback circuit which may be adjusted by well-known means to give proper phase relations and amount of energy fed back so that a two-stage oscillater is set up. The frequency of oscillation will be that of the tuning of OT1, 1500 cycles in this case. The amount of energy fed back is such that condenser C1 is charged and volume limiting action is set up. The oscillator will, therefore, maintain a constant output level because of the volume limiting action of its amplifier.

Relay R15 connects the output of the oscillator through output resistances CR1 and OR2 to the input of the radio transmitter RT'2. As dial D is operated spurts of 150G-cycle tone enter the radio transmitter. Relay R16 when operated puts ground on the leads from switches A.K. and S.H. This operates relay AR switching the antenna to the transmitter RT2, relay R12 removing the plate supply from the receiver RR2 and R14 disabling the selector RS operating circuit. The circuit is thus set up to transmit the dial pulses. When dialing is completed key DK is returned to normal and the circuit is under control of switches A K. and SH. for normal service. It is obvious that the combined transmitting and receiving unit SRU1 may be used with any transmission system either two-wire or four-wire by proper application and, therefore, that its use is not to be confined to the example here given.

We have described Figs. 1, 2, 3 and 4 showing a system of signaling using spurts of 150G-cycle tone. The successful operation of this system through heavy static is somewhat dependent uponhaving tone on only for the dial spurts the amplifier constants being adjusted for maximum eiciency when using spurts. However, the system may be set up to have steady tone on when dialing is in progress and to interrupt that tone by the dial. Such a system under most static conditions will work as effectively as the spurt system. This system will be referred to as the interrupted tone system and this invention should not be coniined to the spurt system, but should be understood to include the interrupted tone system.

Likewise we may set up this signaling system so that each unit of the digit or code is sent by either a marking or a spacing pulse. Such a system is partly spurt and partly interrupted tone since the pause between digits in the code may be either a marking or spacing pulse depending on the preceding digit being odd or even. Fig. 5 shows the dialing arrangements for such a system. The selector key SK operates relay R21 opening the lead A1 B1. A1 B1 will connect to an oscillator or D. C.- control circuit as explained for Fig. 3. When key SK is in its normal position R21 is released. It is controlled by SK to send either a marking or spacing pulse for each unit of the code. Dial D1 normally sends a marking and spacing pulse for each unit of the digit so that pulse dividing relays R22 and R23 are associated with it here. These put out a marking pulse or a spacing pulse for each code unit comprising a, marking and a spacing pulse from D1 as explained in connection with the pulse dividing relays R12 and R12 in Fig. 2. Key K1 when closed as shown a1- ways assures that relay R23 is non-operated and lead A1 B1 closed. Opening K1 permits the dialing from D1.

With this system of pulsing the pulsedividing relays R12 and R13 are no longer required in the signal receiving unit. The selector RS is then controlled directly by relay R11 as shown in Fig. 6. When R11 operates condenser Cs is charged from +200 through CR1, the windings of RS -and the lower contacts of R11 operating RS.

When Ru'releases C3 discharges through CR1, the upper contacts of R11 and the windings of RS operating RS in the opposite direction.

One additional example of the use of a selective signaling unit is illustrated in Fig. 7, in which the features of Figs. 2 and 4 are combined. In this ligure a radio transmitter RT is provided on board ship, and by switching to either of two oscillators OZ and O3, generating frequencies f2 and f3, the transmitter may be used to transmit either to the shore station or to another ship. Two radio receivers are provided on board the ship, the receiver RRz being used to receive from the shore station and the receiver RRz being used to receive from another ship. For signaling between ship and shore the frequency f1 is used from shore to ship and the frequency f2 is used from ship to shore, but in communicating between two ships the same frequency f3 may be used in both directions.

Two antennae A1 and AZ are provided. The antenna A1 is used for both sending and receiving under the control of the key AK, the antenna being connected normally for receiving but being connected to the radio transmitter RT when the key AK is actuated. By means of the key CK the antenna A1 may be connected to either the radio receivery RRZ when communicating with the shore station or to the receiver RR'z when communicating with another vessel. In the stand-by position, antenna A1 is connected to the receiver RRZ to receive signals from the shore station and the antenna AZ is connected toi the receiver RR2 to receive signals fro-m another vessel. When, however, the key CK is operatedin order to establish connection with another vessel, the antenna A1 is connected to the receiver RRZ and the antenna AZ is shifted to the receiver RRZ in order to receive a code signal from the shore station if one should be received while the vessel is communicating with another vessel. The two receivers RR2 and RR'z are connected to two input transformers in series, the transformer INZ being bridged to the output of the receiver RRZ and the transformer INZ being bridged to the output of the receiver RRZ. These two transformers are so poled with respect to the input of ther amplifying arrangements VT1 and VTZ that a static crash reaching theoutputs of the two receivers will balance out if the crash is of equal volume in the two input transformers. As the outputs become unequal the balancingout ei'ect becomes less but the effect of the static crash will nevertheless be of smaller magnitude than if only one receiver were connected to the amplifier.

The operation, in so far as it may not be understood from the previous description of Figs. 2 and 4, is as follows:

With the circuit in the condition shown, the apparatus is arranged to receive from the shore station, the antenna A1 being connected over the back contact of relay AR and the back contact of relay RAR to radio receiver RRZ to the output aoc/4,958 Y of which is connected the operators0 receiver If a code signal corresponding to the ship,

ORz. station is received from the shore station the interrupted tone will be transmitted from the output of the receiver RRZ through the transf former INZ to the input of the amplifier of the receiving unit SRU1. The amplifier rectifying arrangements of the combined transmitting and receiving unit SRU1 operate as described in connection with Fig. 4 tol set the receiving selector RS which will connect the point 2 of the selector to point 5 of the selector, completing aV circuit for the bell BZ over the upper contact of the relay R14. Upon hearing .the bell the operator may actuate the key KZ, thereby energizing relay R14 which opens the bell circuit and reverses the connection to the polar relay of the receiving selector RS to restore the selector to normal, as previously described. The ship operator may then by throwing the key AK talk to the shore station since the radio transmitter is normally supplied with carrier frequency from the oscillator OZ. Whenever the key AK is restored the antenna A1 will be disconnected from the output of the transmitter RT and will be connected to the input of the receiver RRZ so that theship operator may listen to the shore station.`

Should the operator of the ship station desire to call another vessel, the operator will ,throw the key CK, thereby energizing relay RCR, RAR, and OR. Relay OR connects the oscillator O3 to the radio transmitter RT and enables trans-v mission at the frequency f3.. The relay RAR at its left-hand front contact connects the antenna A1 to the radio receiver RRZ, which receives on the frequency f3 used in communicating between ships. At its right-hand front contact the relay RAR connects antenna AZ to the receiver RRZ, thereby acting as a stand-by connection to enable the shore station to send a code signal to the ship during intership communication.

The operator then throws the key DK, actuating the relay R15, to set up an oscillating circuit through the amplifier VT1-VTZ to produce the signaling tone. 'Ihe relay R15 is actuated at the same time to connect the output transformer OT1 to the radio transmitter YRT. By actuating the dial D the tone may be interrupted to send the code combination to call another ship through the radio transmitter RT. At the end of the dialing operation the key DK is restored, thereby returning the amplifying arrangement to its normal amplifying condition and again connecting the transformer OT1 to the rectifying arrangement RR11.

Having called the other ship, the operator may now, by throwing the key AK, connect the antcnna A1 to the radio transmitter RT and transmit to the other ship at the frequency f3. Upon restoring the key AK to normal, the antenna A1 will be connected over the upper contact of the relay AR and the left-hand front contact of the relay RAR to the radio receiver RRZ in order to enable the operator t0y receive from the distant station. In this connection it should be noted that the relay RCR, which was actuated when the key CK was thrown, connects the operators receiver ORZ to the output of the radio receiver RRZ.

When the key CK is restored to normal the relays OR, RAR and RCR are de-energized and the antennae A1 and A2 are connected to the radio receivers RRZ and RRZ, respectively, so that code signals may be received from either should send in a code signal, such code signal would be received at the frequency f3 over the antenna A2 and be transmitted to the radio receiver RR2 whose output is connected through the transformer INz to the combined transmitting and receiving unit SRU. Preferably the code combination transmitted from another ship will be different from that transmitted from the store station in calling the same ship station. The combined transmitting and receiving unit operates as previously described to actuate the selector RS which may connect the points 2 and 3, thereby completing a circuit for the bell Bz over the upper contact of relay R18. Upon hearing the bell Bz the ship operator will actuate the key K22 thereby energizing the relay R18 and reversing the connection through the polar relay of the selector RS, which will be restored to normal. The ship operator will no-w throw the key CK to enable communication with the calling ship by sending over the radio transmitter at the frequency f3 and by receiving over the antenna A1 and the radio receiver RR'z at the same frequency. While this communication is going on, the code signal received from the shore station would come in over the antenna A2 and be received by the receiver RRZ. In such case the combined transmitting and receiving unit which is not used during voice transmission would receive the code signal through the transformer IN2 and the selector RS would be actuated as before to ring the bell B2.

It will be obvious that the general principles herein disclosed may be embodied in many other organizations widely different from those illustrated without departing from the spirit of the invention as defined in the following claims.

What is claimed is:

1. In a signal transmission system, a master station, a plurality of associated stations, means at said master station to transmit calling code signals individual to each associated station, means at individual associated stations to transmit calling code signals to other associated stations, said calling codes transmitted by said master station and said associated stations being converted into audible tone wave groups, separate receivers at each associated station for picking up signals from the master station and signals from other associated stations, a wave converter at each associated station to convert received tone waves to code signals, said receivers being connected to said Wave converter in opposing relation, and signal responsive means associated with said converter.

2. In a signal transmission system, two signal receiving circuits adapted respectively to receive independent signals on corresponding diierent frequencies, an amplier common to both circuits, said amplier having a dinerent gain when signaling current is present than it has in the absence of signaling current, and a common indicator associated with said circuits, said circuits being connected with opposite effect to said indicator whereby they will give a null response for static.

3. In a signal transmission system, a master station comprising a radio transmitter and a radio receiver, a plurality of associated stations l each comprising two antennas, two radio receivers and a radio transmitter, one receiver being normally connected and adapted to receive signals through one antenna from the master station, the other receiver being normally connected and adapted to receive signals through the other antenna from other associated stations, and means under the control of an operator at an associated station to change these connections for signaling between such associated station and the master station or another associated station and for talking with either such station.

4. In a signal transmission system, two receiving circuits adapted respectively to receive waves of different frequencies from diierent parts of the spectrum of voice and static frequencies, an amplier common to both circuits, said amplifier having a different gain when signaling current is present than it has in the absence of signaling current, a common indicator associated with said circuits, said circuits being connected with opposite effect to said indicator, and means for sending signals on one of said frequencies to be received by the appropriate receiving circuit of the said two receiving circuits.

EDMUND R. TAYLOR.

CHARLES C. TAYLOR.

'PAUL W. WADSWORTH. 

